Unsullied means still clean, still pure, not yet spoiled or dirtied by anything. It carries a strong feeling that something could easily have been ruined — and was not. That is the heart of the word: it is not simply 'clean', it is 'kept safe from being made dirty'. Most often the dirt is not real dirt. It is used about reputations, names, records, memories, ideals: 'his reputation was unsullied by the scandal', 'an unsullied record of service'. Look at that little word 'by' — unsullied by X names the thing that might have stained it, and this is the pattern you will see again and again. It can also describe physical purity in a poetic way — unsullied snow, unsullied water — but that use belongs to literature, not to talking about your kitchen floor. This is an old and formal word. You will meet it in novels, in speeches, in obituaries, sometimes in a courtroom. It is also faintly old-fashioned, so a writer choosing it is usually choosing a slightly grand tone on purpose. The base verb, 'sully', means to make dirty or to damage someone's good name; you will see it in 'sully his reputation'.